Pretty sure we hold it, I've just went through every Second Division season in England and Middlesbrough scored 122 goals in 42 games in the 1926/27 season, with George Camsell managing 59 of them by himself.
The closest to that is Everton managing 121 goals in 1930/31, but there's nobody else close.
I'm surprised the club haven't made a bigger deal about it, assuming the record on Wikipedia are accurate, but I suppose it's less impressive when it's the second division.
I haven't looked at the stats, but I'm sure I've seen Kebano's name in the goalscoring column quite a few times this season. Shame we didn't get goals out of him, but then we didn't get many goals out of anyone while he was here.